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<h2 align=center>read</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
<p>
read - read data from file
</p>

<h3>Library</h3>
<p>
Standard C Library (libc, -lc)
</p>

<h3>Synopsis</h3>
<p>
<tt>#include &lt;unistd.h&gt;</tt><br>
<br>
<tt>ssize_t</tt><br>
<tt>read(int </tt><em>fd</em><tt>, void *</tt><em>buf</em><tt>,
size_t </tt><em>buflen</em><tt>);</tt>
</p>

<h3>Description</h3>
<p>
<tt>read</tt> reads up to <em>buflen</em> bytes from the file
specified by <em>fd</em>, at the location in the file specified by the
current seek position of the file, and stores them in the space
pointed to by <em>buf</em>. The file must be open for reading.
</p>

<p>
The current seek position of the file is advanced by the number of
bytes read.
</p>

<p>
Each read (or <A HREF=write.html>write</A>) operation is atomic
relative to other I/O to the same file.
Note that the kernel is not obliged to (and generally cannot) make the
read atomic with respect to other threads in the same process
accessing the I/O buffer during the read.
</p>

<h3>Return Values</h3>
<p>
The count of bytes read is returned. This count should be
positive. A return value of 0 should be construed as signifying
end-of-file. On error, <tt>read</tt> returns -1 and sets
<A HREF=errno.html>errno</A> to a suitable error code for the error
condition encountered.
</p>

<p>
Note that in some cases, particularly on devices, fewer than
<em>buflen</em> (but greater than zero) bytes may be returned. This
depends on circumstances and does not necessarily signify
end-of-file.
</p>

<h3>Errors</h3>
<p>
The following error codes should be returned under the conditions
given. Other error codes may be returned for other cases not
mentioned here.

<table width=90%>
<tr><td width=5% rowspan=3>&nbsp;</td>
    <td width=10% valign=top>EBADF</td>
			<td><em>fd</em> is not a valid file descriptor, or was
			not opened for reading.</td></tr>
<tr><td valign=top>EFAULT</td>
			<td>Part or all of the address space pointed to by
			<em>buf</em> is invalid.</td></tr>
<tr><td valign=top>EIO</td>
			<td>A hardware I/O error occurred reading the
			data.</td></tr>
</table>
</p>

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